Automated super-cooled water-droplet size differentiation using aircraft accretion patterns

ABSTRACT

Apparatus and associated methods relate to determining, based on a spatial extent of ice accretion, whether an atmosphere contains super-cooled water droplets that equal and/or exceed a predetermined size. A convex-shaped housing is mounted to an aircraft and exposed to an airstream. The convex-shaped housing has a testing region that is monitored for ice accretion by an ice detector. A boundary locator determines a specific location to be tested within the testing region. The determined specific location corresponds to a calculated boundary that separates an ice-accretion region from an ice-free region if the atmosphere contains super-cooled water droplets up to the predetermined size. If the ice detector detects ice accretion at the determined specific location, an alert is generated. The alert can advantageously inform a pilot of an atmosphere containing super-cooled water droplets that equal or exceed the predetermined size.

BACKGROUND

Certain atmospheric conditions can lead to ice formation on aircraftsurfaces. Ice formation on aircraft surfaces can increase the weight ofthe aircraft and can increase the drag of the aircraft. Increasingeither the weight or the drag of an aircraft can result in a stall speedthat is higher than it would otherwise be in an ice-free condition. Iceformation on lifting surfaces can result in a decrease in a wing's liftand/or a decrease in a propeller's thrust. Ice formation can also affectthe controllability of an aircraft by affecting the airflow over controlsurfaces, such as ailerons.

Various atmospheric conditions can cause more or less ice formation onan aircraft. For example, water droplet density, total moisture content,air temperature, water droplet temperature, droplet size distribution,etc. all factor into risk of ice formation. Some atmospheric conditionscan present little or no risk of ice formation on an aircraft.

Various aircraft flying conditions can affect locations and/or amountsof ice formation on aircraft surfaces. For example, airspeed, angle ofattack, angle of side-slip, and presence of de-icing equipment allfactor into location and/or risk of ice formation.

Some aircraft have been equipped with equipment intended to obtainmetrics of the atmosphere so as to predict whether the atmospherepresents a risk of ice-formation on exterior surfaces. Ice formation onaircraft surfaces can be visually perceived by the pilot, should the iceform on a surface within view of the cockpit window.

SUMMARY

Apparatus and associated devices relate to a super-cooled water-dropletsize measurement system. The super-cooled water-droplet size measurementsystem includes a housing having a convex exterior surface. The housingis configured to be mounted to an aircraft so as to expose the convexexterior surface to an airstream of the aircraft in flight. Thesuper-cooled water-droplet size measurement system includes an icedetector configured to detect ice accretion at a plurality of testlocations within a testing region of the convex exterior surface. Iceaccretes, in conducive conditions, on at least an ice-accretion portionof the testing region. The super-cooled water-droplet size measurementsystem also includes a boundary locator configured to determine aspecific one of the plurality of test locations within the testingregion of the convex exterior surface. The determined specific one ofthe plurality of test locations corresponds to a boundary that separatesthe ice-accretion portion of the testing region and an ice-free portionof the testing region in conditions that include the atmosphere havingsuper-cooled water droplets up to a predetermined maximum size.

Some embodiments relate to a method for generating an alert in responseto atmosphere exterior to an aircraft having super-cooled water dropletsexceeding a predetermined size. The method includes exposing a housingto an airstream of an aircraft, the housing having a convex exteriorsurface. The method includes determining a test location within atesting region of the convex exterior surface. The test locationcorresponds to a calculated boundary that separates the ice-accretionportion of the testing region and an ice-free portion of the testingregion in conditions that include an atmosphere having super-cooledwater droplets exceeding the predetermined size. The method includesmonitoring the determined test location within the testing region todetect whether ice accretes at the monitored test location. The methodincludes generating an alert signal in response to ice accretion beingdetected at the monitored test location within the testing region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an aircraft equipped with an exemplaryautomated super-cooled-water-droplet size differentiation system.

FIG. 2 is a schematic diagram of ice accreting on a leading edge of acurved member in an airstream.

FIG. 3 is a schematic diagram depicting different zones of ice-accretionassociated with different sizes of super-cooled water droplets.

FIG. 4 is a graph of exemplary relations of size of an ice-accretionregion versus size of super-cooled water droplets.

FIG. 5 is a block diagram of an exemplary ice-accretion alert system.

FIG. 6 is a flow chart of an exemplary method for generating an alert ifatmosphere exterior to an aircraft has super-cooled water dropletsexceeding a predetermined size.

FIG. 7 is a schematic view of an exemplary super-cooled water-dropletsize measurement system that is attachable to an aircraft.

FIG. 8 is a graph depicting a size span of water-droplets vs. locationalong a chord of a convex-shaped housing.

DETAILED DESCRIPTION

Apparatus and associated methods relate to determining, based on aspatial extent of ice accretion, if an atmosphere contains super-cooledwater droplets that equal or exceed a predetermined size. A testingregion on an exterior surface of an aircraft is monitored for iceaccretion by an ice detector. A boundary calculator determines aspecific location to be tested within the testing region. The determinedspecific location corresponds to a calculated boundary that shouldseparate an ice-accretion region from an ice-free region if theatmosphere contains super-cooled water droplets of no larger than thepredetermined size. If the ice detector detects ice accretion at thedetermined specific location, an alert is generated. The alert canadvantageously inform a pilot of the aircraft that the atmospherecontains super-cooled water droplets that equal or exceed thepredetermined size.

FIG. 1 is a schematic view of an aircraft equipped with an exemplaryautomated super-cooled water-droplet size differentiation system. InFIG. 1, aircraft 10 has been equipped with super-cooled water-dropletsize differentiator system 12. Super-cooled water-droplet sizedifferentiator system 12 includes testing region 14, ice detector 16,ice boundary calculator 18 and alert system 20. In the depictedembodiment, testing region 14 includes a portion of an exterior surfaceof aircraft 10. When aircraft 10 is flying through a cloud that hassuper-cooled water droplets, ice can form on exterior surfaces ofaircraft 10.

As will be described below, if conditions permit, ice preferentiallyforms at different locations on these exterior surfaces. Ice tends toform on leading edges of aircraft 10 and is less likely to form as theair moves more and more aft of these leading edges. Ice tends to formincreasingly aft of the leading edge as the atmosphere containssuper-cooled water droplets of increasing size. Testing region 14 can beselected such that ice will accrete on a portion of testing region 14 ifthe atmosphere contains super-cooled water droplets of a predeterminedsize. Various embodiments may use various testing regions. In someembodiments, testing region 14 may be located on the fuselage ofaircraft 10, for example. In some embodiments, testing region 14 may belocated on an airfoil, such as a wing or tail, of aircraft 10. In someembodiments, testing region 14 may be located on some appendage ofaircraft 10.

In the depicted embodiment, testing region 14 includes a side window ofthe cockpit of aircraft 10. Testing region 14 is monitored by icedetector 16. Various types of ice detectors can be used in variousembodiments. In some embodiments ice detector 16 can be a visual lightcamera. In some embodiments, ice detector 16 can be an infrared camera,for example. In some embodiments, a series of spot sensors may be usedto detect ice accretion. Ice formation at an aft location within testingregion 14 may be indicative of an atmosphere having super-cooled waterdroplets equal to or exceeding a predetermined size.

The specific aft location within testing region 14 that is indicative ofan atmosphere having super-cooled water droplets equal to or exceedingthe predetermined size can be affected by various conditions. Some suchconditions that affect the indicative aft location include: aircraftparameters; flying parameters; and atmospheric conditions. Ice boundarycalculator 18 calculates the indicative aft location based on one ormore of these conditions. Various types of ice boundary calculators canbe used in various embodiments. For example, in some embodiments, iceboundary calculator 18 may perform fluid dynamic computations tocalculate the indicative aft location. In some embodiments, a look-uptable may be used to determine the indicative aft location, for example.

If ice detector 16 detects ice accretion at the indicative aft locationcalculated by ice boundary calculator 18, then alert system 20 generatesan alert signal. In various embodiments, various types of alert signalsmay be generated. For example, in some embodiments an audible alertsignal may be generated. In some embodiments, an alert signal may be inthe form of an electrical signal sent to a display device. For example,a display monitor may present an optical image of the testing regionalong with a flashing alert signal. In some embodiments, an alert signalmay be in the form of a signal to another aircraft system. The signalmay be provided as either a simple alert or it may be provided withadditional information regarding the size of super-cooled water dropletsin the atmosphere outside the aircraft.

FIG. 2 is a schematic diagram of ice accreting on a leading edge of acurved member in an airstream. In FIG. 2, three-dimensional airfoil 22is shown in cross section. Airfoil 22 has flow-dividing axis 24 alignedwith a general direction of airflow. Airflow is represented by flowvectors 26 a, 26 b, 26 c, 26 d. Water droplets 28 a, 28 b are carried bythe airflow. Small water droplets 28 a generally follow the flowvectors, because a mass of the small water droplets 28 a is small. Amomentum of the small water droplets 28 a is correspondingly small,because of the small mass. Because the momentum is small for small waterdroplets, changing the direction, and thus the momentum, of these smallwater droplets can be achieved by small forces, such as those impartedby flow vectors 26 a, 26 b, 26 c, 26 d. Small water droplets 28 aimpinge airfoil 22 only proximate flow-dividing axis 24 at leading edge30.

Large water droplets 28 b, however, have momentums that are larger thanthose of small water droplets 28 a, due to larger masses of the largewater droplets 26 b. Such large water droplets 28 b do not follow flowvectors 26 a, 26 b, 26 c, 26 d as readily as do small water droplets 28a. Because large water droplets 28 b more readily cross flow vectors 26a, 26 b, 26 c, 26 d, such large water droplets 28 b impinge airfoil 22along a greater section of leading edge 30 than is impinged by smallwater droplets 28 a. Large water droplets 28 b impinge airfoil 22proximate flow-dividing axis 24 at leading edge 30 as do small waterdroplets 28 a. Large water droplets 28 b also impinge airfoil 22 aft ofleading edge 30 for a distance that is related to the droplet size.Airflow does impart a force on large water droplets 28 b, and thereforelarge water droplets 28 b do experience momentum change. Because largewater droplets 28 b can undergo such momentum change, these large waterdroplets impinge airfoil 22 only over a limited range about leading edge30.

If water droplets 28 a, 28 b are super-cooled (e.g., at temperaturesbelow a freezing temperature of water), then such particles can freezeupon impact with airfoil 22 or another object (e.g., a fuselage, etc.).Pure water can be super-cooled without freezing in the absence of anucleation site. Such a scenario is not infrequent in cloud atmospheres.The shock of impingement and/or the structural nucleation sitespresented by the impinging object can cause such super-cooled waterdroplets to freeze almost immediately upon such an impingement event.

FIG. 3 is a schematic diagram depicting different zones of ice-accretionassociated with different sizes of super-cooled water droplets. In FIG.3, airfoil 22 depicted in FIG. 2 is shown in magnification todemonstrate a relationship between water droplet size and impingementregion. Two different impingement regions 32, 34 are depicted proximateleading edge 30 of airfoil 22. Impingement region 32 corresponds to asmall region about leading edge 30.

Small impingement region 32 is a region in which water droplets, whichare less than or equal to a relatively small size (such as small waterdroplets 28 a depicted in FIG. 2), can impinge, for a given set ofaircraft and flying conditions. Small water droplets 28 a can readilyfollow flow vectors 26 a, 26 b, 26 c, 26 d (depicted in FIG. 2). Flowvectors 26 a, 26 b show an airflow pattern above airfoil 22, and flowvectors 26 c, 26 d show an airflow pattern below airfoil 22. Flowvectors 26 a, 26 b diverge from flow vectors 26 c, 26 d about centralaxis 24. Only at locations along leading edge 30 that are proximatecentral axis 24 can small water droplets 28 a impinge airfoil 22. Theintersection of leading edge 30 and flow-dividing axis 24 can be calledthe stagnation point.

Large impingement region 34 includes portions of airfoil 22 which can beimpinged only by water droplets that are larger than a predeterminedsize (such as large water droplets 28 b depicted in FIG. 2) for a givenset of aircraft and flying conditions. Because larger water droplets 28b can cross flow vectors 26 a, 26 b, 26 c, 26 d more readily than cansmall water droplets 28 a, such large water droplets 28 b impingeairfoil 22 within larger region (e.g., large impingement region 34)about leading edge 30 than the region (e.g., small impingement region32) impinged by small water droplets 28 a. In this way, FIG. 3demonstrates a relation that exists between a size of water droplets anda regional area in which such sized water droplets are capable ofimpingement.

FIG. 4 is a graph of exemplary relations of size of an ice-accretionregion versus size of super-cooled water droplets. In FIG. 4, graph 32has horizontal axis 34 and vertical axis 36. Horizontal axis 34represents maximum size D_(MAX) of water droplets in an atmosphere.Vertical axis 36 represents a distance dimension (e.g., angle θ fromstagnation point or chord length d from the stagnation point) ofimpingement region. Graph 32 has three relations 38 a, 38 b, 38 c.Relation 38 a represents a relation between maximum size D_(MAX) ofwater droplets and distance dimension of impingement region for a firstset of icing conditions. Relations 38 b, 38 c represent relationsbetween maximum size D_(MAX) of water droplets and distance dimension ofimpingement region for a second and a third set of icing conditions,respectively.

Parameters that affect icing conditions can include aircraft conditions,flying conditions, and atmospheric conditions, for example. Aircraftconditions can include, for example, a shape of a structure to whichwater droplets impinge, temperature of a surface of the impingementregion, aircraft configuration, etc. Flying conditions can include, forexample, an angle of attack, an angle of side-slip, an airspeed, waterdroplet temperature, liquid water content, etc. Atmospheric conditionscan include air temperature, air pressure, etc. Various embodiments maybe more or less affected by one or more of the icing conditions. Forexample, some embodiments may be more or less sensitive to angle ofattack. A structure that presents substantially the same shape to theairflow independent of angle of attack, for example, may be not verysensitive to angle of attack. Some geometries may be less sensitive toangle of sideslip, for example.

FIG. 5 is a block diagram of an exemplary ice-accretion alert system. InFIG. 5, ice-accretion alert system 40 includes controller 42, icedetector 44 and testing region 46 of exterior surface 48 of an aircraft.Controller 42 includes processor(s) 50, ice detector interface 52,aircraft interface 54, storage device(s) 56, user input devices 58, anduser output devices 60. Storage device(s) 56 has various storage ormemory locations. Storage device(s) 56 includes program memory 62,conditions data memory 64, boundary calculation module 66, and alertmodule 68. Controller 42 is in communication with ice detector 44. Icedetector 44 is configured to monitor ice accretion on testing region 46.Testing region 46 is depicted with ice-accretion portion 70 upon whichice has accreted.

As illustrated in FIG. 5, controller 42 includes processor(s) 50, icedetector interface 52, aircraft interface 54, storage device(s) 56, userinput devices 58, and user output devices 60. However, in certainexamples, controller 42 can include more or fewer components. Forinstance, in examples where controller 42 is an avionics unit,controller 42 may not include user input devices 58 and/or user outputdevices 60. In some examples, such as where controller 42 is a mobile orportable device such as a laptop computer, controller 42 may includeadditional components such as a battery that provides power tocomponents of controller 42 during operation.

Processor(s) 50, in one example, is configured to implementfunctionality and/or process instructions for execution withincontroller 42. For instance, processor(s) 50 can be capable ofprocessing instructions stored in storage device(s) 56. Examples ofprocessor(s) 50 can include any one or more of a microprocessor, acontroller, a digital signal processor (DSP), an application specificintegrated circuit (ASIC), a field-programmable gate array (FPGA), orother equivalent discrete or integrated logic circuitry.

Storage device(s) 56 can be configured to store information withincontroller 42 during operation. Storage device(s) 56, in some examples,is described as computer-readable storage media. In some examples, acomputer-readable storage medium can include a non-transitory medium.The term “non-transitory” can indicate that the storage medium is notembodied in a carrier wave or a propagated signal. In certain examples,a non-transitory storage medium can store data that can, over time,change (e.g., in RAM or cache). In some examples, storage device(s) 56is a temporary memory, meaning that a primary purpose of storagedevice(s) 56 is not long-term storage. Storage device(s) 56, in someexamples, is described as volatile memory, meaning that storagedevice(s) 56 do not maintain stored contents when power to controller 42is turned off. Examples of volatile memories can include random accessmemories (RAM), dynamic random access memories (DRAM), static randomaccess memories (SRAM), and other forms of volatile memories. In someexamples, storage device(s) 56 is used to store program instructions forexecution by processor(s) 50. Storage device(s) 56, in one example, isused by software or applications running on controller 42 (e.g., asoftware program implementing long-range cloud conditions detection) totemporarily store information during program execution.

Storage device(s) 56, in some examples, also include one or morecomputer-readable storage media. Storage device(s) 56 can be configuredto store larger amounts of information than volatile memory. Storagedevice(s) 56 can further be configured for long-term storage ofinformation. In some examples, storage device(s) 56 include non-volatilestorage elements. Examples of such non-volatile storage elements caninclude magnetic hard discs, optical discs, flash memories, or forms ofelectrically programmable memories (EPROM) or electrically erasable andprogrammable (EEPROM) memories.

Ice detector interface 52, in some examples, includes a communicationsmodule. Ice detector interface 52, in one example, utilizes thecommunications module to communicate with external devices via one ormore networks, such as one or more wireless or wired networks or both.The communications module can be a network interface card, such as anEthernet card, an optical transceiver, a radio frequency transceiver, orany other type of device that can send and receive information. Otherexamples of such network interfaces can include Bluetooth, 3G, 4G, andWi-Fi 33 radio computing devices as well as Universal Serial Bus (USB).

Aircraft interface 54 can be used to communicate information betweencontroller 42 and an aircraft. In some embodiments, such information caninclude aircraft conditions, flying conditions, and/or atmosphericconditions. In some embodiments, such information can include dataprocessed by controller 42, such as, for example, alert signals.Aircraft interface 54 can also include a communications module. Aircraftinterface 54, in one example, utilizes the communications module tocommunicate with external devices via one or more networks, such as oneor more wireless or wired networks or both. The communications modulecan be a network interface card, such as an Ethernet card, an opticaltransceiver, a radio frequency transceiver, or any other type of devicethat can send and receive information. Other examples of such networkinterfaces can include Bluetooth, 3G, 4G, and Wi-Fi 33 radio computingdevices as well as Universal Serial Bus (USB). In some embodiments,communication with the aircraft can be performed via a communicationsbus, such as, for example, an Aeronautical Radio, Incorporated (ARINC)standard communications protocol. In an exemplary embodiment, aircraftcommunication with the aircraft can be performed via a communicationsbus, such as, for example, a Controller Area Network (CAN) bus.

User input devices 58, in some examples, are configured to receive inputfrom a user. Examples of user input devices 58 can include a mouse, akeyboard, a microphone, a camera device, a presence-sensitive and/ortouch-sensitive display, push buttons, arrow keys, or other type ofdevice configured to receive input from a user. In some embodiments,input communication from the user can be performed via a communicationsbus, such as, for example, an Aeronautical Radio, Incorporated (ARINC)standard communications protocol. In an exemplary embodiment, user inputcommunication from the user can be performed via a communications bus,such as, for example, a Controller Area Network (CAN) bus.

User output devices 60 can be configured to provide output to a user.Examples of user output devices 60 can include a display device, a soundcard, a video graphics card, a speaker, a cathode ray tube (CRT)monitor, a liquid crystal display (LCD), a light emitting diode (LED)display, an organic light emitting diode (OLED) display, or other typeof device for outputting information in a form understandable to usersor machines. In some embodiments, output communication to the user canbe performed via a communications bus, such as, for example, anAeronautical Radio, Incorporated (ARINC) standard communicationsprotocol. In an exemplary embodiment, output communication to the usercan be performed via a communications bus, such as, for example, aController Area Network (CAN) bus.

FIG. 6 is a flow chart of an exemplary method for generating an alert ifatmosphere exterior to an aircraft has super-cooled water dropletsexceeding a predetermined size. In FIG. 6, method 100 is depicted fromthe vantage point of processor(s) 50 of FIG. 5. Method 100 begins atstep 102 where processor(s) 50 initializes index I. Then, at step 104,processor(s) 50 receives, from the aircraft, aircraft conditionsincluding airspeed A(I), angle of attack AOA(I), and angle of side-slipAOS(I). The method then proceeds to step 106 where processor(s) 50receives, from the aircraft, atmospheric conditions includingtemperature T(I) and pressure P(I). The method proceeds to step 108where processor(s) 50 retrieves, from data memory, a maximum waterdroplet size D_(MAX).

The method then proceeds to step 110 where processor(s) 50 calculates aboundary location B(I) based on the received aircraft conditions, A(I),AOA(I), and AOS(I), the received atmospheric conditions, T(I) and P(I),and the retrieved maximum water droplet size D_(MAX). Then at step 112,processor(s) 50 determines a location TL(I) within a testing region thatcorresponds to the calculated boundary location B(I). Method 100proceeds to step 114 where processor(s) 50 receives, from the icedetector 44 (depicted in FIG. 5) a signal indicative of ice formation atthe determined location TL(I). Processor(s) 50 evaluates whether ice hasformed at the determined location TL(I) based on the received signal.If, at step 114, processor(s) 50 determine that ice has not formed atthe determined location TL(I), then at step 116 processor(s) 50 clearsthe alert signal ALERT. If, however, at step 114, processor(s) 50determine that ice has formed at the determined location TL(I), then atstep 118 processor(s) 50 sets the alert signal ALERT. Method 100proceeds from steps 116 and/or 118 to step 120, at which processor(s) 50increment index I. Then, method 100 returns to step 104 and repeats.

In some embodiments, the output of an ice-accretion detection system candetermine a maximum super-cooled water-droplet size based on a measuredextent of ice formation on an exterior surface of the aircraft. Theice-accretion detection system can provide, as an output, a signalindicative of the determined maximum super-cooled water-droplet size.This output signal may then be used by a receiving system to determinewhether an alert signal is generated.

In an exemplary embodiment, a super-cooled water-droplet sizedistribution of an atmosphere exterior to an aircraft can be calculated.Distinct locations on an exterior surface of an aircraft may besusceptible to ice accretion arising from super-cooled water dropletsexceeding a predetermined size striking the distinct location. Forexample, ice may form at each distinct location, only if the atmosphereexternal to the aircraft includes super-cooled water droplets thatexceed the predetermined size corresponding to that distinct location.By measuring a rate of ice accretion at a plurality of locations along achord from the stagnation point toward an aft location, a water-dropletsize distribution can be calculated.

For example, ice may accrete at a boundary location that separates anice-accretion region from an ice-free region due to an atmosphere thathas super-cooled water-droplets up to a maximum size. Only thesuper-cooled water droplets that are of the maximum size may causeice-accretion at the boundary location. And then, at locations moreforward from the boundary location, ice may accrete due to super-cooledwater-droplets that have sizes that span between a lower threshold andthe maximum size. As one travels toward the stagnation point, iceaccretes due to a span of sizes of super-cooled water droplets thatincludes smaller and smaller sizes. By measuring the amount and/or therate of ice accretion at each of these points, a reconstruction of asuper-cooled water-droplet size distribution can be calculated

In some embodiments, a heating system is repeatedly used to melt,evaporate, and/or sublimate ice accreted on the testing region. Such aheating system can facilitate testing in conditions in which iceaccretion slows or stops due to improving atmospheric conditions. Aftermelting or sublimating any accreted ice from the testing region, theheater may be turned off so that ice may again accrete if conditionspermit such accretion. In an exemplary embodiment, the heater can beoperated cyclically, such that each cycle has a heating portion, and iceaccretion portion, and an ice detection portion. The heater can beactivated during the heating portion and deactivated during the iceaccretion and ice detection portions. Such an embodiment may repeatedlyevaluate ice accretion so as to provide current icing data to a user.

In an exemplary embodiment, a testing region of an exterior surface ofan aircraft is monitored for ice accretion. The testing region can belocated such that it includes a location upon which ice can accrete onlyif super-cooled water droplets of a size that exceeds a predeterminedtesting limit are present. If ice accretes in such a location, then analert signal may be generated. In some embodiments the testing regionwill present a convex shape to the atmosphere. In some embodiments, theexterior surface of the aircraft will be intentionally shaped so as toinclude locations upon which ice can accrete only if super-cooled waterdroplets of a size that exceeds a predetermined testing limit arepresent. For example, a bubble may be formed in a side window of acockpit. The bubble may project out of the side window, for example, topresent a convex shape to the outside atmosphere.

In various embodiments, various exterior surfaces of an aircraft may beused as testing regions for ice accretion. For example, in someembodiments, a propeller spinner may be used as an ice-accretion testingregion. In some embodiments, a leading edge of a rescue hoist may beused as an ice-accretion testing region. In some embodiments, a strutcan be used as an ice-accretion testing surface, for example.

FIG. 7 is a schematic view of an exemplary super-cooled water-dropletsize measurement system that is attachable to an aircraft. In FIG. 7,super-cooled water-droplet size measurement system 62 is attached toaircraft 64 outside of cockpit 66. Super-cooled water-droplet sizemeasurement system 62 has housing 68 that includes a convexforward-facing exterior surface so as to expose the convexforward-facing exterior surface to an airstream of aircraft 64 when inflight. When so exposed to an airstream atmosphere that includessuper-cooled water-droplets, ice can accrete on the convexforward-facing surface.

A control system can be located within housing 68. The control systemcan determine locations where ice accretes on the convex forward-facingexterior surface. In some embodiments, the control system can receivesignals from a series of spot sensors located on the convexforward-facing exterior surface of housing 68. In some embodiments, acamera can be located within housing 68. In some embodiments, a laserbased system can probe an exterior surface for ice accretion Housing 68can include transparent and/or translucent materials. Portions of theconvex forward-facing exterior surface that have ice accreted thereonmay image differently than portions of the convex forward-facingexterior surface that are ice free, for example.

The control system may determine, based on an extent of the iceaccretion portion of the convex forward-facing exterior surface, amaximum size of super-cooled water-droplets. In some embodiments, thecontrol system may determine, based on a rate of ice accretion and/or ameasured amount of ice accretion at multiple locations of the convexforward-facing exterior surface, a super-cooled water-dropletdistribution in the atmosphere. The control system can then communicatethe calculated information (e.g., maximum size, distribution, orsuper-cooled water-droplets) to the aircraft and/or pilot, for example.In an exemplary embodiment, the control system may generate an alert ifthe maximum size of super-cooled water-droplets is determined to begreater than a predetermined threshold.

In some embodiments, the housing is rigidly attached to an aircraft insuch a way that the housing has a fixed orientation with respect to theaircraft. In such embodiments, the stagnation point can be a function offlying conditions. For example, the stagnation point can change as afunction of airspeed, angle of attack, angle of sideslip, etc. As thestagnation point changes, the location of the boundary that separatesthe ice-accretion portion of the testing region from the ice-freeportion of the testing region can also change. If a housing issemi-hemispherical or hemispherical in shape, various flying conditionsby locating the point of symmetry of the ice-accretion region. Bylocating the boundary that separates the ice-accretion portion of thetesting region from the ice-free portion of the testing region onopposite sides of the stagnation point, however, the flying conditionscan be determined, as well as the maximum super-cooled water dropletsizes. For example, by testing opposite lateral sides of the stagnationpoint, an angle of sideslip can be determined. And by testing oppositevertical sides of the stagnation point, an angle of attack can bedetermined. In both such cases, a maximum size of super-cooled waterdroplets in the cloud atmosphere can be determined.

In some embodiments, the housing is attached to an aircraft in anon-rigid fashion, so as to permit the housing to orient a leading edgeof the housing so that it is the stagnation point under various flyingconditions. For example, by mounting the housing using a gimballedtelescope assembly, the orientation of the leading edge can be changedin response to changing flying conditions. In some embodiments, aweathervane type of mounting system can facilitate an automaticorientation of the housing in response to variations in flyingconditions. For example, one or more fins can be coupled to a trailingend of the housing.

Various flying conditions can cause variations in local cooling ofexterior surfaces of the aircraft and of the housing. For example, localvariations in airspeed proximate surfaces of the aircraft can causelocal cooling variations. Ice formation conditions can therefore varylocally as well. For example, the icing conditions of the housing maynot be exactly the same as the icing conditions of a control surface ofan aircraft. In some embodiments, a temperature control system cancontrol a temperature of the housing, so as to better align icingconditions of the housing with those of various control surfaces of theaircraft to which the housing is attached. In some embodiment, thetemperature control system can be used simply to ensure that theexterior surface of the aircraft is cool enough to cause icing so that amaximum droplet size can be determined. For example, a cooling systemcan be configured to actively cool the convex exterior surface of thehousing.

Such temperature control systems can also be used to heat the testingregions so as to sublimate, melt, and/or evaporate ice accreted to suchregions. Such temperature control capabilities can be used to providecycles of operation that include a heating portion, an accretionportion, and a sensing portion. The heater can be activated during theheating portion to remove any ice accreted to the testing region. Theheater can then be deactivated during the accretion portion and duringthe sensing portions. In some embodiments, the testing region can becooled, before or during the accretion and/or sensing portions. The icedetector can then be activated during the sensing portion. Someembodiments can include an alert system to generate an alert if the icedetector detects ice at testing locations indicative of super-cooledwater droplets having sizes that exceed a predetermined threshold.

FIG. 8 is a graph depicting a size span of water-droplets vs. locationalong a chord of a convex-shaped housing. In FIG. 8, graph 200 hashorizontal axis 202 and vertical axis 204. Horizontal axis 202represents location along a chord of a convex exterior surface exposedto an atmosphere containing super-cooled water droplets. Vertical axis204 represents a size of the super-cooled water droplets. Graph 200includes droplet size/location relation 206 corresponding to a size ofsuper-cooled droplets that can strike the convex exterior surface at theindicated location. For example, at a given location along theconvex-shaped housing (e.g., draw a vertical line from a given x-axislocation), the exterior surface of the convex-shaped housing will beimpinged by droplets exceeding some minimum size up until the maximumsized droplet contained in the cloud atmosphere. Line 212 identifies therelation corresponding to the predetermined minimum size of super-cooledwater droplets that contribute to ice accretion vs. location along thechord of the convex shaped housing. Droplets smaller than the minimumsize will follow the airflow vectors and will not impinge theconvex-shaped housing at the given location. Dashed line 214 identifiesthe maximum size of super-cooled water droplets contained in the cloudatmosphere.

For a given size of a super-cooled water droplet (e.g., draw ahorizontal line from a give y-axis location), the exterior surface ofthe convex-shaped housing will be impinged for the stagnation point upto a maximum impingement location corresponding to the given size ofsuper-cooled water droplet. Point 208 of relation 206 corresponds to theboundary location separating an ice accretion portion and an ice-freeportion of the convex exterior surface for the cloud atmosphere havingthe maximum size of super-cooled water droplet corresponding to dashedline 214. Not all sizes of particles, however, contribute to iceaccretion at every location within the ice accretion portion of theconvex exterior surface. At point 208, relation 206 indicates that onlysuper-cooled water droplets equal to the maximum size (or greater if thecloud atmosphere had greater sized particles) accrete at the boundarylocation. The region to the right of point 208 on graph 200 correspondsto the ice-free portion of the convex exterior surface, and points tothe left of point 208 correspond to the ice-accretion portion of theconvex exterior surface.

Vertical line 210 of relation 206 corresponds to the stagnation point ofthe convex exterior surface. At the stagnation point corresponding tovertical line 210, super-cooled water droplets of all sizes within theatmosphere contribute to ice accretion. Between point 208 and verticalline 210, super-cooled water droplets that have a size greater than apredetermined minimum will contribute to ice accretion. Super-cooledwater droplets smaller than the predetermined minimum size will followthe flow vector lines and not impinge the convex exterior surface, andtherefore will not contribute to ice accretion. Line 212 identifies therelation corresponding to the predetermined minimum size of super-cooledwater droplets that contribute to ice accretion vs. location along thechord of the convex shaped housing.

The following are non-exclusive descriptions of possible embodiments ofthe present invention.

A super-cooled water-droplet size measurement system includes a housinghaving a convex exterior surface. The housing is configured to bemounted to an aircraft so as to expose the convex exterior surface to anairstream of the aircraft in flight. The super-cooled water-droplet sizemeasurement system includes an ice detector configured to detect iceaccretion at a plurality of test locations within a testing region ofthe convex exterior surface. Ice accretes, in conducive conditions, onat least an ice-accretion portion of the testing region. Thesuper-cooled water-droplet size measurement system also includes aboundary locator configured to determine a specific one of the pluralityof test locations within the testing region of the convex exteriorsurface. The determined specific one of the plurality of test locationscorresponds to a boundary that separates the ice-accretion portion ofthe testing region and an ice-free portion of the testing region inconditions that include the atmosphere having super-cooled waterdroplets up to a predetermined maximum size.

The super-cooled water-droplet size measurement system of the precedingparagraph can optionally include, additionally and/or alternatively, anyone or more of the following features, configurations and/or additionalcomponents: an alert system; a gimballed mounting mechanism; one or morefins; a cooling system; a droplet-size calculator; a droplet-sizedistribution calculator; and a heater. The alert system can beconfigured to generate, in response to detection by the ice detector ofice accretion at the determined specific one of the plurality of testlocations, an alert. The gimballed mounting mechanism can facilitateorientation of the housing such that a leading edge of the housing canbe directed toward the airstream. The one or more fins can be coupled toan aft end of the housing. The cooling system can be configured toactively cool the convex exterior surface of the housing. Thedroplet-size calculator can be configured to calculate a plurality ofwater-droplet sizes, each corresponding to one of the plurality of testlocations of the testing region. Each of the calculated water-dropletsizes can correspond to a droplet size, below which water droplets donot cause ice to accrete at the corresponding test location. Thedroplet-size distribution calculator can be configured to calculate,based on the detected ice accretion rate at the plurality of testlocations, a super-cooled water-droplet size distribution. The heatercan be configured to heat the testing region so as to melt, evaporateand/or sublimate any ice accreted thereto.

A further embodiment of the foregoing super-cooled water-droplet sizemeasurement system, wherein the ice detector can include a cameraconfigured to mount external to the housing and configured to obtainimages of the testing region. A further embodiment of any of theforegoing super-cooled water-droplet size measurement systems, whereinthe housing can include a transparent or translucent shell. The icedetector can include a camera mounted internal to the housing andconfigured to obtain images, through the transparent or translucentshell, of the testing region. A further embodiment of the foregoingsuper-cooled water-droplet size measurement system, wherein the alertsystem can be configured to provide cycles of operation that include aheating portion, an accretion portion and a sensing portion of each ofthe provided cycles. The heater can be activated during the heatingportion, and the heater can be deactivated during the accretion andsensing portions. The ice detector can be activated during the sensingportion. A further embodiment of the foregoing super-cooledwater-droplet size measurement system, wherein the convex exteriorsurface can be semi-hemispherical. The super-cooled water dropletmeasurement system can further include an angle-of-attack calculatorconfigured to calculate an angle-of-attack and/or angle-of-sideslipbased on a vertical and/or horizontal extent of ice accretion onopposite sides of a centerline of the convex exterior surface of thehousing.

A method for generating an alert in response to atmosphere exterior toan aircraft having super-cooled water droplets exceeding a predeterminedsize includes exposing a housing to an airstream of an aircraft, thehousing having a convex exterior surface. The method includesdetermining a test location within a testing region of the convexexterior surface. The test location corresponds to a calculated boundarythat separates the ice-accretion portion of the testing region and anice-free portion of the testing region in conditions that include anatmosphere having super-cooled water droplets exceeding thepredetermined size. The method includes monitoring the determined testlocation within the testing region to detect whether ice accretes at themonitored test location. The method includes generating an alert signalin response to ice accretion being detected at the monitored testlocation within the testing region.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components: calculating aplurality of water-droplet sizes; and calculating an accretion rate at aplurality of test locations. Each of the calculated plurality ofwater-droplet sizes can correspond to one of a plurality of testlocations of the testing region. Each of the calculated water-dropletsizes can corresponds to a droplet size, below which water droplets donot contribute to ice accretion at the corresponding test location.Calculation of the super-cooled water-droplet size distribution can bebased on a detected ice accretion rate at the plurality of testlocations, a super-cooled water-droplet size distribution.

A further embodiment of any of the foregoing methods, whereindetermining the test location within the testing region includescalculating flying conditions base on ice accretion being detected onopposite sides of a stagnation point. A further embodiment of any of theforegoing methods, wherein determining the test location within thetesting region includes calculating the test location usingcomputational fluid dynamics. A further embodiment of the foregoingmethod, wherein determining the test location within the testing regionincludes calculating a test location based on at least one of: airspeed;angle of attack; angle of sideslip; and total air temperature. A furtherembodiment of the foregoing method, wherein monitoring the determinedtest location includes imaging the test region using a camera. A furtherembodiment of the foregoing method, wherein monitoring the determinedtest location further includes processing a test pixel of an imageobtained by the camera, the test pixel imaging the determined testlocation.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

The invention claimed is:
 1. A super-cooled water-droplet sizemeasurement system comprising: a housing having a convex exteriorsurface, the housing configured to be mounted to an aircraft so as toexpose the convex exterior surface to an airstream of the aircraft inflight; an ice detector configured to detect ice accretion at aplurality of test locations within a testing region of the convexexterior surface, wherein ice accretes, in conducive conditions, on atleast an ice-accretion portion of the testing region; a boundary locatorconfigured to prospectively calculate a specific one of the plurality oftest locations within the testing region of the convex exterior surface,the determined specific one of the plurality of test locationscorresponding to a boundary that separates the ice-accretion portion ofthe testing region and an ice-free portion of the testing region inconditions that include the atmosphere having super-cooled waterdroplets up to a predetermined maximum size, wherein the test locationis calculated based on at least one of: airspeed; angle of attack; angleof sideslip; and total air temperature; and a gimballed mountingmechanism that facilitates orientation of a leading edge of the housingin response to changing flying conditions.
 2. The super-cooledwater-droplet size measurement system of claim 1, further comprising: analert system configured to generate, in response to detection by the icedetector of ice accretion at the determined specific one of theplurality of test locations, an alert.
 3. The super-cooled water-dropletsize measurement system of claim 2, wherein the alert system isconfigured to provide cycles of operation that include a heatingportion, an accretion portion and a sensing portion of each of theprovided cycles, wherein the heater is activated during the heatingportion, and the heater is deactivated during the accretion and sensingportions, and the ice detector is activated during the sensing portion.4. The super-cooled water-droplet size measurement system of claim 1,further comprising one or more fins coupled to an aft end of thehousing.
 5. The super-cooled water-droplet size measurement system ofclaim 1, further comprising a cooling system configured to actively coolthe convex exterior surface of the housing.
 6. The super-cooledwater-droplet size measurement system of claim 1, further comprising: adroplet-size calculator configured to calculate a plurality ofwater-droplet sizes, each corresponding to one of the plurality of testlocations of the testing region, wherein each of the calculatedwater-droplet sizes correspond to a droplet size, below which waterdroplets do not cause ice to accrete at the corresponding test location.7. The super-cooled water-droplet size measurement system of claim 6,further comprising: a droplet-size distribution calculator configured tocalculate, based on the detected ice accretion rate at the plurality oftest locations, a super-cooled water-droplet size distribution.
 8. Thesuper-cooled water-droplet size measurement system of claim 1, whereinthe ice detector comprises a camera configured to mount external to thehousing and configured to obtain images of the testing region.
 9. Thesuper-cooled water-droplet size measurement system of claim 1, whereinthe housing comprises a transparent or translucent shell, wherein theice detector comprises a camera mounted internal to the housing andconfigured to obtain images, through the transparent or translucentshell, of the testing region.
 10. The super-cooled water-droplet sizemeasurement system of claim 1, further comprising a heater configured toheat the testing region so as to melt, evaporate and/or sublimate anyice accreted thereto.
 11. The super-cooled water-droplet sizemeasurement system of claim 1, wherein the convex exterior surface issemi-hemispherical, the super-cooled water droplet measurement systemfurther comprising an angle-of-attack calculator configured to calculatean angle-of-attack and/or angle-of-sideslip based on an extent of iceaccretion on opposite sides of a centerline of the convex exteriorsurface of the housing.
 12. A method for generating an alert in responseto atmosphere exterior to an aircraft having super-cooled water dropletsexceeding a predetermined size, the method comprising: exposing ahousing to an airstream of an aircraft, the housing having a convexexterior surface; orienting, via a gimballed mounting mechanism, aleading edge of the housing in response to changing flying conditions;prospectively calculating a test location within a testing region of theconvex exterior surface, the test location corresponding to a calculatedboundary that separates the ice-accretion portion of the testing regionand an ice-free portion of the testing region in conditions that includean atmosphere having super-cooled water droplets exceeding thepredetermined size; monitoring the calculated test location within thetesting region to detect whether ice accretes at the monitored testlocation; and generating an alert signal in response to ice accretionbeing detected at the monitored test location within the testing region.13. The method of claim 12, wherein determining the test location withinthe testing region comprises: calculating flying conditions base on iceaccretion being detected on opposite sides of a stagnation point. 14.The method of claim 12, wherein the test location is calculated usingcomputational fluid dynamics.
 15. The method of claim 12, wherein thetest location is calculated based on at least one of: airspeed; angle ofattack; angle of sideslip; and total air temperature.
 16. The method ofclaim 12, wherein monitoring the determined test location comprises:imaging the test region using a camera.
 17. The method of claim 16,wherein monitoring the determined test location further comprises:detecting whether ice accretes at the monitored test location based on atest pixel of an image obtained by the camera, the test pixel imagingthe determined test location.
 18. The method of claim 12, furthercomprising: calculating a plurality of water-droplet sizes, eachcorresponding to one of a plurality of test locations of the testingregion, wherein each of the calculated water-droplet sizes correspondsto a droplet size, below which water droplets do not contribute to iceaccretion at the corresponding test location.
 19. The method of claim18, further comprising: calculating, based on a detected ice accretionrate at the plurality of test locations, a super-cooled water-dropletsize distribution.
 20. The super-cooled water-droplet size measurementsystem of claim 7, further comprising: an alert system configured togenerate, in response to detection by the ice detector of ice accretionat the determined specific one of the plurality of test locations; analert; wherein the alert provides additional information regarding thesize of the supercooled water droplets in the atmosphere outside of theaircraft.